Analytical & Bioanalytical Electrochemistry
Volume:10 Issue: 8, Aug 2018

Herein, a very simple and scalable electrochemical strategy is reported to fabricate reduced graphene oxide (rGO)-Mn3O4 nanoparticles composite for supercapacitors. First, graphene oxide is directly produced via Hummers method, and dispersed in manganese nitrate aqueous solution. The rGO-Mn3O4 particles nanocomposite is then prepared through electrochemically decoration of Mn3O4 nanoparticles onto reduced graphene oxide (rGO) sheets. The formation of composite is explained by electrophoretic/electrochemical deposition (EPD/ECD) mechanism. The as-prepared rGO-Mn3O4 nanocomposite is characterized by XRD, IR, FE-SEM and TEM techniques. These analyses results specified the co-deposition of manganese oxide particles and rGO sheets on the cathode electrode. The charge storage ability of the fabricated nanocomposite as electrode material for supercapacitors was studied using cyclic voltammetry and charge-discharge techniques. The obtained electrochemical data indicated that the rGO-Mn3O4 nanocomposite enable to provide specific capacitance of 364 F g−1 at 2 A g−1 and 86.3% of its initial capacity after 5000 charge/discharging.

The electro-oxidation of Catechol in presence of L-Histidine has been investigated in aqueous solution with various pH values, different electrodes and different concentration of L-Histidine by using cyclic voltammetry, differential pulse voltammetry and controlled potential coulometry. Electrochemically generated o-benzoquinone (Michael acceptor) from oxidation of Catechol reacts with lower concentration of L-Histidine as nucleophiles in the second scan of potential. The products obtained from the reaction are assumed to be 2-((3,4dioxocyclohexa-1,5-dien-1-yl)amino)-3-(1H-imidazol-4-yl)propanoic acid that undergo electron transfer at more negative potentials than the Catechol. The effect of pH of Catechol in presence of L-Histidine has been studied by varying pH from 5 to 11. The concentration effect of L-Histidine with the fixed concentration of Catechol (2 mM) was measured from 2 mM to 100 mM. The reaction was strongly influenced by the pH as well as concentration of L-Histidine. The reaction is mostly favorable in 30 mM of L-Histidine and 2 mM of Catechol at pH 7. The behavior of the reaction mechanism was of ECE type.

Here we describe a simple and novel electrochemical synthesis for preparation of Mn doped iron oxide nanoparticles (MIOs) and their surface coating with saccharides (i.e. glucose, sucrose and starch). The electrochemical preparation of MIOs samples were carried out in a two-electrode electrochemical set up including graphite anode and stainless steel cathode. The surface coating with saccharide agents was also performed in the same set up and simultaneously with the formation of iron oxide particles on the cathode surface. The fabricated MIOs were specified through FT-IR, FE-SEM, XRD, DSC-TGA, and VSM analyses. The structural data obtained by XRD proved the magnetite (Fe3O4) crystal phase of samples, and FT-IR and TG data showed the Mn doping and saccharide coat on the surface of the deposited MIONs. The FE-SEM observations and EDS data confirmed the particle morphology and magnetite chemical composition as well as Mn ions doping into the MIONs. The superparamagnetic nature and suitable magnetic ability (i.e. high saturation magnetization, negligible remanent magnetization and coercivity) for the fabricated MIONs were also assessed though vibrating sample magnetometer (VSM) results. These characters of the electrosynthesized sample provided their suitability for biomedical applications.

MnO2 incorporated Ni-P electrodes were prepared by electroless deposition from a solution containing MnO2 particle suspended by stirring. The electrocatalytic activity of the electrode towards ethanol oxidation found to vary with concentrations of MnO2 particles. The electrode with 10 g/L MnO2 particles exhibited maximum electrocatalytic activity. The optimized electrode had a response time of 14 s and a sensitivity of 8.6 µA/ppm cm2. The electrochemical characterization for the catalytic activity was explained by cyclic voltammetry, chronoamperometry. The sensing behavior of the electrode was studied in 0.2 M NaOH solution containing ethanol using impedance spectroscopy. The maximum rate of ethanol oxidation was observed at its sensing potential.

A sensor based on carbon paste electrode (CPE) modified with benzoylferrocene (BF) and NiO nanoparticls (NiO/NPs) was used for the highly sensitive voltammetric and electrocatalytic measurement of hydrochlorothiazide (HCT) and folic acid (FA). The NiO/NPs were synthesized via a direct chemical precipitation method and were characterized with X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. The obtained sensor represented a suitable and powerful electron mediating behavior along with excellent-separated oxidation peaks of HCT and FA. The acquired peak currents from square wave voltammetry (SWV) technique were linearly dependent on HCT and FA concentrations in the ranges of 1.0–500.0 and 50.0–500.0 µmolL-1 with limits of detection equal to 0.14 and 4.3 µmolL-1, respectively. This mediator/nanoparticle modified electrode was applied for the detection and measurement of HCT and FA in pharmaceutical and biological samples.

Lactate level being an important parameter is to be monitored in body regularly. During acute conditions it elevation may result in heart failure, hepatic disease, sepsis, tissue hypoxia and many more. A simple and sensitive biosensor has been fabricated by immobilizing lactate dehydrogenase enzyme. It was covalently immobilized on the nanocomposite based working electrode. The developed biosensor showed optimal response at pH 7.5, temperature 30℃, response time was 8s with the substrate concentration of 600 µM, the oxidation peak was obtained at 0.66 V which is at a low potential, Km and Imax values for newly fabricated biosensor were 66.7 µM and 153.8 µA respectively. It possessed lower detection limit of 0.015 mM with storage stability of 3 months. A good correlation has been observed when developed method is compared with standard enzyme kit method proving reliability of the method. Blood samples were successfully screened for lactate concentration using working electrode. The newly developed biosensor is less time consuming, accurate, reliable, less costly, requires no sample pre-treatment, screen large number of samples, suitable for on field determination of lactate concentration and finally reusable due to covalently immobilized enzyme.

Dimethyl methyl Phosphonate (DMMP) was used as a flame retardant to reduce the flammability of the electrolyte with minimum negative impact on the electrochemical performance of the electrodes. The flammability and thermal stability of prepared electrolyte in the presence of DMMP by different contents were evaluated using self-extinguishing time (SET), differential scanning calorimeter (DSC). Linear Sweep voltammetry (LSV) and galvanostatic charge and discharge tests were carried out to investigate the effect of DMMP on the electrochemical properties. When a sample containing 5 vol.% DMMP is used as electrolyte in 18650 cell, the cell exhibits quite good cycling stability; like the Blank electrolyte with capacity fade after 55 cycles at 0.1 C is 92.68 and 96.59%, respectively. The cathode electrode interface is characterized with EIS, SEM, and XRD, DSC after several charge/discharge cycles which demonstrate stable and liner protective film is formed on the surface of cathodes in the presence of 5 vol.% DMMP. The results imply that DMMP is a promising option as highly flame-retardant and electrochemically compatible electrolyte additive for safe lithium-ion batteries.

A graphite pencil electrode was used as a working electrode in the analysis of dopamine and serotonin by voltammetric techniques. The electrochemical investigations were carried out at a graphite pencil electrode at a scan rate of 0.05 Vs-1 in a 0.2 M phosphate buffer solution. The electrochemical behavior of dopamine shows two redox pairs while the electrooxidation of serotonin shows irreversible behavior at a graphite pencil electrode at a scan rate of 0.05 Vs-1. A graphite pencil electrode shows excellent results for dopamine and serotonin when combined and acts as very good sensor for dopamine in the presence of serotonin.

An electrochemical method for determination of sulfite has been developed using Schiff base modified graphite screen printed electrodes as a disposable chemosensor. The modified graphite screen printed electrode was characterized with voltammetry. Differential pulse voltammogram of modified SPE in the presence of sulfite showed a characteristic peak current at 350 mV. A linear response of the sensor was observed in the concentration range of 0.5-300.0 µM of the analyte. The limit of detection (LOD) was found to be 0.3 μM for sulfite. The method has been used for the determination of sulfite in the natural water samples. These analytical figures of merit evidence the outstanding performance of the modified electrode, which was also successfully applied to the determination of sulfite in environmental and biological samples.

This paper reports a new citrate-selective electrode based on mono- and di-nuclear copper (II) complexes that bear a salicylaldehyde-semi-carbazone tridentate Schiff bases ligand. The electrode serves as a membrane carrier for citrate anions. The performance of the electrode is investigated using potentiometric technique. The results of potentiometry indicate that the developed electrode has a Nernstian slope of 19.7±0.3 mV in a linear concentration range of 1.0×10-7-1.0×10-1 M, a detection limit of 6.3×10-8 M, an applied pH range of 8.0-12.0, and a response time of less than 15 seconds. It can also be used for 21 days without any considerable divergence of potentials.